German Published Patent Application No. 10 2004 027 085 A1 describes a method for keeping a vehicle inside the lane, in which the instantaneous potential hazard is ascertained based on objective and subjective criteria and measures are taken in steps depending on the extent of an impending danger. The objective hazard situation may be ascertained with the aid of a surroundings sensor system in the vehicle by detecting objects situated on the roadway. The behavior of the driver plays a role with the subjective hazard situation, in particular the present level of fatigue, which is ascertained from the steering activity and/or the driving of the vehicle in the lane. A fatigued state is inferred from only minimal steering and pedal movements, while active participation in traffic is to be inferred from a high steering activity. Depending on the overall potential hazard, influence is exerted in a stepped manner, in which initially only information is provided, subsequently a warning is issued, and finally an active intervention in the vehicle is carried out, for example by actuating a steering actuator.